Re: [PATCH resend RFC 2/9] s390/gmap: don't unconditionally call pte_unmap_unlock() in __gmap_zap()

Claudio Imbrenda
2021-09-14T16:52:46Z

On Thu, 9 Sep 2021 18:22:41 +0200
David Hildenbrand <david@redhat.com> wrote:

> ... otherwise we will try unlocking a spinlock that was never locked via a
> garbage pointer.
>
> At the time we reach this code path, we usually successfully looked up
> a PGSTE already; however, evil user space could have manipulated the VMA
> layout in the meantime and triggered removal of the page table.
>
> Fixes: 1e133ab296f3 ("s390/mm: split arch/s390/mm/pgtable.c")
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
> arch/s390/mm/gmap.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index b6b56cd4ca64..9023bf3ced89 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -690,9 +690,10 @@ void __gmap_zap(struct gmap *gmap, unsigned long gaddr)
>
> /* Get pointer to the page table entry */
> ptep = get_locked_pte(gmap->mm, vmaddr, &ptl);
> - if (likely(ptep))
> + if (likely(ptep)) {
> ptep_zap_unused(gmap->mm, vmaddr, ptep, 0);
> - pte_unmap_unlock(ptep, ptl);
> + pte_unmap_unlock(ptep, ptl);
> + }
> }
> }
> EXPORT_SYMBOL_GPL(__gmap_zap);